1. Field of the Invention
This invention relates to a color combining optical system and a projection type display apparatus constituted by this color combining optical system, and more particularly to a projection type display apparatus for combining images modulated by three liquid crystal panels illuminated, for example, by lights of three primary colors, i.e., blue, green and red, and forming a color image on a screen, a wall or other surface capable of displaying.
2. Related Background Art
Heretofore, when the combination of three colors is to be effected by the use of a color combining prism and a projection lens, it has been difficult to make three projected images completely coincident with one another because there is the chromatic aberration of magnification of the projection lens. In view of such a problem, in Japanese Patent Application Laid-Open No. 8-201756, there is made a proposition changing the focal length or the disposed position of a field lens disposed between color combining means comprised of two dichroic mirrors and a reflecting mirror, and a liquid crystal panel discretely in each optical path to thereby make the chromatic aberration of magnification of a projection lens correctable. Likewise in Japanese Patent Application Laid-Open No. 11-231218, there is made a proposition for disposing a correction lens between a color combining prism comprised of a cross dichroic prism and a liquid crystal panel to thereby make the chromatic aberration of magnification of a projection lens correctable.
In the apparatus of the above-mentioned Japanese Patent Application Laid-Open No. 8-201756, however, two dichroic mirrors and a reflecting mirror are used as color combining means, and in addition to the chromatic aberration of magnification of the projection lens, the distortion of the surfaces of the dichroic mirrors and the distortion of a color channel transmitted through the surfaces of the dichroic mirrors by the dichroic mirrors occur and therefore, the size of the projected image of each channel has not become a size expected from calculation, and the aberration correction of each channel could not be effected well. Particularly, in a color channel using the reflecting surfaces of the dichroic mirrors, the change in the magnification of the projected image by the distortion of the surfaces of the dichroic mirrors is great, and when the distortion of the surfaces of the dichroic mirrors is asymmetrical, the projected image on a screen also assumes an asymmetrical shape correspondingly thereto and therefore, even if the focal length or the position of the field lens is changed discretely in each color channel, it has been difficult to superpose the projected images completely upon one another.
Also, in the apparatus of the above-mentioned Japanese Patent Application Laid-Open No. 11-231218, a cross dichroic prism comprised of four right-angled triangular pole prisms is used for color combining and therefore, in addition to the chromatic aberration of magnification of the projection lens, the surface of the dichroic mirror is bent by the angular error of the prism and therefore, the deformation of the projected images is added, and it has been difficult to superpose the projected images of three colors, i.e., red, green and blue, completely upon one another on a screen.
It is an object of the present invention to solve the above-noted problems and to provide a projection type display apparatus which suffers little from the occurrence of the distortion of the surface of a dichroic mirror in a color combining optical system and the occurrence of the deformation of a projected image by the angular deviation of the surface of the dichroic mirror and in which the correction of the chromatic aberration of magnification of a projection lens is stably possible during mass production.
In one aspect of the present invention, there is provided a color combining optical system which includes:
at least three prisms;
two dichroic mirror layers for reflecting lights differing in wavelength area from each other, the two dichroic mirror layers being formed so as not to intersect with each other with the prism adjacent to one of the three prisms which is located most adjacent to the light exit side interposed therebetween; and
at least one optical element having positive or negative refractive power, the optical element receiving light from at least one of a plurality of light modulating elements, and causing the light to enter one of the at least three prisms;
wherein the light exit surface of the prism located most adjacent to the light exit side serves also as a total reflection surface for reflecting the light to one of the two dichroic mirror layers.
In another aspect of the present invention, there is provided a color combining optical system which includes:
at least three prisms; and
two dichroic mirror layers for reflecting lights differing in wavelength area from each other, the two dichroic mirror layers being formed so as not to intersect with each other with the prism adjacent to one of the three prisms which is located most adjacent to the light exit side interposed therebetween;
wherein the light exit surface of the prism located most adjacent to the light exit side serves also as a total reflection surface for reflecting light to one of the two dichroic mirror layers, and at least one of the light incidence surfaces of the three prisms has positive or negative refractive power.
In another aspect of the present invention, there is provided a color combining optical system which includes:
at least three prisms; and
two dichroic mirror layers for reflecting lights differing in wavelength area from each other, the two dichroic mirror layers being formed so as not to intersect with each other with the prism adjacent to one of the three prisms which is located most adjacent to the light exit side interposed therebetween;
wherein the light exit surface of the prism located most adjacent to the light exit side serves also as a total reflection surface for reflecting light to one of the two dichroic mirror layers, and the at least three prisms have therein an area having positive or negative refractive power.
In another aspect of the present invention, there is provided a color combining optical system which includes:
at least four prisms;
two dichroic mirror layers for reflecting lights differing in wavelength area from each other, the dichroic mirror layers being formed so as not to intersect with each other with a set of prisms adjacent to one of the four prisms which is located most adjacent to the light exit side interposed therebetween; and
an optical element having positive or negative refractive power, the optical element receiving light from at least one of a plurality of light modulating means, and causing the light to enter one of the at least four prisms;
wherein the light exit surface of the prism located most adjacent to the light exit side serves also as a total reflection surface for reflecting the light to one of the two dichroic mirror layers.
In another aspect of the present invention, there is provided a color combining optical system which includes:
at least four prisms; and
two dichroic mirror layers for reflecting lights differing in wavelength area from each other, the dichroic mirror layers being formed so as not to intersect with each other with a set of prisms adjacent to one of the four prisms which is located most adjacent to the light exit side interposed therebetween;
wherein the light exit surface of the prism located most adjacent to the light exit side serves also as a total reflection surface for reflecting the light to one of the two dichroic mirror layers, and at least one of the light incidence surfaces of the at least four prisms has positive or negative refractive power.
In another aspect of the present invention, there is provided a color combining optical system which includes:
at least four prisms; and
two dichroic mirror layers for reflecting lights differing in wavelength area from each other, the two dichroic mirror layers being formed so as not to intersect with each other with a set of prisms adjacent to one of the four prisms which is located most adjacent to the light exit side interposed therebetween;
wherein the light exit surface of the prism located most adjacent to the light exit side serves also as a total reflection surface for reflecting the light to one of the two dichroic mirror layers, and the at least four prisms have therein an area having positive or negative refractive power.
In further aspect of the above-described optical system, on the premise that one of the four prisms which is located most adjacent to the light exit side is the first prism, the set of prisms are the second and third prisms as counted from the light exit side.
In further aspect of the above-described optical system, on the premise that one of the four prisms which is located most adjacent to the light exit side is the first prism, the second and third prisms as counted from the light exit side have positive or negative refractive power therebetween.
In further aspect of the above-described optical system, on the premise that one of the four prisms which is located most adjacent to the light exit side is the first prism, there is an optical element having positive or negative refractive power on the light incidence side of the second prism as counted from the light exit side.
In further aspect of the above-described optical system, on the premise that one of the four prisms which is located most adjacent to the light exit side is the first prism, there is an optical element having positive or negative refractive power on the light exit side of the third prism as counted from the light exit side.
In further aspect of the above-described optical system, on the premise that one of the four prisms which is located most adjacent to the light exit side is the first prism, a first dichroic mirror layer for reflecting a first color light is formed between the first and second prisms as counted from the light exit side, and a second dichroic mirror layer for reflecting a second color light is formed between the third and fourth prisms as counted from the light exit side.
In another aspect of the present invention, there is provided a projection type display apparatus which includes:
a plurality of light modulating means for modulating a plurality of color lights differing in wavelength area from one another;
color combining means for combining the plurality of color lights modulated by the light modulating means; and
projecting means for enlarging and projecting the lights combined by the color combining means.
In further aspect of the above-described projection type display apparatus, the optical element having positive or negative refractive power or the incidence surfaces of the prisms having positive or negative refractive power are disposed between at least blue light modulating means of the plurality of light modulating means and the color combining optical system.
In further aspect of the above-described projection type display apparatus, the following conditional expression is satisfied:
xe2x80x830.03 less than L/bf less than 0.3,
where L: the air-converted interval between the display portion of the light modulating means and the principal point of the optical element having positive or negative refractive power;
bf: the back focal length of the projecting means on the reduction conjugate side thereof when the conjugate length of the projecting means on the enlargement conjugate side thereof is infinity.
In further aspect of the above-described projection type display apparatus, the following conditional expression is satisfied:
|fw/fc| less than 0.03,
where fw: the focal length of the projecting means;
fc: the focal length of the optical element.
In another aspect of the present invention, there is provided a projection type display apparatus which includes:
a plurality of light modulating means for modulating a plurality of color lights differing in wavelength area from one another;
color combining means for combining the plurality of color lights modulated by the light modulating means; and
projecting means for enlarging and projecting the lights combined by the color combining means.
In further aspect of the above-described projection type display apparatus, blue light modulating means of the plurality of light modulating means is disposed in opposed relationship with the light incidence surface of the prism located most adjacent to the light exit side.
In further aspect of the above-described projection type display apparatus, the following conditional expression is satisfied:
0.45 less than L/bf less than 0.8,
where L: the air-converted interval between the display portion of the light modulating means and the principal point of the optical element;
bf: the back focal length of the projecting means on the reduction conjugate side thereof when the conjugate length of the projecting means on the enlargement conjugate side thereof is infinity.
In further aspect of the above-described projection type display apparatus, the following conditional expression is satisfied:
|fw/fc| less than 0.015,
where fw: the focal length of the projecting means;
fc: the focal length of the optical element.